Among other alloys, particularly the bronze casting (CAC406) excels in castability, corrosion resistance, machinability and pressure resistance and, when molten, exhibits satisfactory flowability and, therefore, is suitable for cast parts with fairly complicated shapes. Thus, it has been being copiously used hitherto in the general plumbing hardware, such as valves, cocks and joints
The CAC406 is used in copious amounts in water-contacting fittings for the plumbing hardware of this kind because it allows easy manufacture of wholesome castings and particularly excels in machinability owing to containing Pb in a weight ratio of about 5%.
When this bronze alloy is used for the material of water-contacting fittings, such as valves, the lead that is contained in the bronze castings in a state only sparingly reduced to a solid solution is eluted into the ambient water and consequently suffered to deteriorate the quality of the water. This phenomenon grows in prominence particularly when water stagnates in the water-contacting fittings.
Thus, the development of the so-called leadless copper alloy is underway at present. The efforts directed toward the development have resulted in proposing a number of improved alloys.
Typical examples thereof will be described hereinafter.
For example, a leadless copper alloy that acquires exalted machinability and allows prevention of dezincification by incorporating Bi in the place of lead into the copper alloy has been proposed (refer to pages 2-3 of JP-B HEI 5-63536).
A leadless bronze that enjoys exalted machinability in consequence of adding Ca to BC6 (CAC406), for example, thereby chiefly forming compounds with P (CaP, Ca3P2) and giving birth to an action of refining chips has been proposed (refer to pages 2-3 and FIG. 2 of Japanese Patent No. 2949061).
In this case, the precipitation of intermetallic compounds of CaP characterizes the production of the leadless bronze. The actual use of this product is difficult because Ca is an active metal and the addition of Ca into a copper alloy therefore results in inducing vigorous oxidation and markedly lowering the yield.
As another example, a leadless bronze that has exalted the mechanical strength thereof by adding Sb and consequently suppressing the occurrence of porosity during the course of casting due to the addition of Bi directed toward enhancing machinability has been proposed (refer to pages 3-6 of Japanese Patent No. 2889829). In this case, the addition of Ni is directed toward fortifying the matrix and preventing segregation.
As yet another example, a bronze cast material that has the crystal thereof refined as a substitution type intermetallic compound by the addition of Ti and has the crystal grain boundary strength thereof fortified as a penetration type intermetallic compound by the addition of B has been proposed (refer to pages 2-10 of Japanese Patent No. 2723817).
As still another example, a leadless free-cutting bronze alloy that has the machinability and the anti-seizing property thereof enhanced by the addition of Bi and has the anti-dezincification and the mechanical properties thereof acquired securely by the addition of Sn, Ni and P has been proposed (refer to pages 3-4 of JP-A 2000-336442).
As a further example, a bronze alloy that has the mechanical properties and the machinability thereof equalized with those of the CAC406 by adding Se and Bi to thereby particularly induce precipitation of a Se—Zn compound has been proposed (refer to columns 1-4 of U.S. Pat. No. 5,614,038).
Though the leadless bronze alloy materials proposed as described above invariably secure the specified magnitudes (tensile strength of 195 N/mm2 or more and elongation of 15% or more) of a bronze alloy of JIS H5120 (CAC406), the aforementioned properties which the CAC 406 materials distributed in the market exhibit are in much greater magnitudes than those specified by JIS, such as tensile strength in the neighborhood of 240 N/mm2 and elongation in the neighborhood of 33%. Thus, an alloy that is capable of securing mechanical properties and machinability equal to those secured by the materials circulating in the market has not been developed in the prior art mentioned above. Such is the existing state of affairs.
Then, the leadless bronze alloy mentioned above has added thereto Se, Bi, etc. as alternative components for Pb. Since these alternative components are expensive rare elements, the desirability of developing an alloy that secures the aforementioned properties in magnitudes equal to those of the CAC406 in the materials distributed in the market while the amounts of the rare elements to be added are decreased has been finding recognition.
Further, the leadless bronze alloy mentioned above has been proposed with a view to exalting mechanical properties and machinability. Pb, however, is a component that contributes to the wholesomeness of a casting. The question how the leadless bronze alloy secures the wholesomeness of a casting has not yet been elucidated.
This invention has been developed in consequence of a diligent study. It is aimed at providing a copper-based alloy that acquires mechanical properties at least equal to the bronze alloy (CAC406) generally used hitherto while securing machinability equal to the CAC406 in spite of a decrease in the content of rare elements (such as Bi and Se) in the alloy in consequence of exactly comprehending the true properties of the elements (such as Bi and Se) which are alternative components for Pb, realizes suppression of the occurrence of casting defects by elucidating the unresolved influence of the decrease of the alternative components (such as Bi and Se) for Pb on the wholesomeness of a casting, and further enables inexpensive production by decreasing the rare elements and is also aimed at providing a cast ingot and a liquid-contacting part each using the alloy.